DS200CTBDG1A | GE Mark V Board | Thermocouple

Description

Product Introduction

The GE DS200CTBDG1A is a thermocouple input module for the Mark V Speedtronic turbine control system. It provides per-channel galvanic isolation for critical temperature measurements. This module is used where grounded thermocouples or electrical noise would otherwise corrupt readings.

Core advantage: The G1A revision isolates each of the 8 thermocouple inputs from the backplane and from each other (1,500 V RMS channel-to-backplane, 500 V channel-to-channel). Standard CTBA modules (CTBAG1A) have bank isolation – one grounded thermocouple can corrupt all 16 channels. With the CTBDG1A, a ground fault on channel 3 leaves channels 1,2,4-8 fully operational. Field data from generators with high stray currents shows CTBDG1A boards reduce temperature measurement errors from 5-10°C to <0.5°C.

Key Technical Specifications

Key Selling Points & Differentiators

• Per-channel galvanic isolation – Standard CTBA (16-channel) has no isolation between channels. A grounded TC at turbine potential (voltage difference) causes massive error. CTBDG1A eliminates ground loops.
• Individual CJC per channel – Each of the 8 inputs has its own cold junction compensation thermistor. No cross-channel interference. Standard boards share one CJC per 8 channels.
• High common mode voltage tolerance – ±250 V. Direct connection to grounded thermocouples on generators or motors. No external isolators needed.
• 8 channels (not 16) – Trade-off for isolation. You get half the channel density but 10x better noise rejection.
• 120 dB CMRR – Rejects 60 Hz common mode noise from VFDs, generators, and welding equipment.
• Live tested with 100 V common mode – We inject 100 VAC (60 Hz) between each TC input and backplane ground. Board must maintain ±1°C accuracy.
• 30-day warranty with cross-ship – Isolation failure or CJC drift? We send replacement same day.

Frequently Asked Questions (FAQ)

Q: What is the difference between DS200CTBAG1A (16-channel) and DS200CTBDG1A (8-channel)?
A: Isolation and channel count. CTBAG1A: 16 channels, no per-channel isolation, shared CJC. CTBDG1A: 8 channels, per-channel galvanic isolation, individual CJC per channel. Pick CTBDG1A for grounded thermocouples, generators, or high-noise environments. Pick CTBAG1A for ungrounded TCs in clean environments where high channel density is needed.

Q: Can I replace a CTBAG1A with a CTBDG1A?
A: Yes – electrically and mechanically compatible. However, you lose 8 channels (16 down to 8). You must reconfigure the I/O map in Toolbox to remove channels 9-16. Takes 15 minutes. Also, the CTBDG1A draws 580 mA vs 420 mA – check backplane 5 V budget.

Q: How do you test per-channel isolation on refurbished boards?
A: We apply 1,500 V AC for 1 second between each TC input and the backplane connector. Leakage current must stay <5 mA. Then we apply 500 V DC between channel 1 and channel 2 (and all adjacent pairs). Leakage must stay <10 µA. About 15% of incoming CTBDG1A boards fail isolation – isolation transformers or optocouplers damaged. Those are scrapped (not repairable).

Q: I see a CTBDG1A board with a yellow sticker near the terminal block. What does that mean?
A: The yellow sticker indicates the board received an additional “common mode sweep” test from 0-250 VAC at 50 Hz, 60 Hz, and 400 Hz. The board must maintain ±1°C accuracy across the sweep. Standard boards tested at 60 Hz only. Yellow-sticker boards are for variable frequency drive (VFD) environments (wide frequency range). We charge an extra $25 for yellow-sticker boards.

Q: My CTBDG1A board reads correctly on channels 1-4 but has 5°C offset on channels 5-8. What failed?
A: The DC-DC converter for the second isolation bank (channels 5-8) has failed. Each group of 4 channels has its own isolated power supply. The converter output may be low (e.g., 4.5 V instead of 5 V), affecting ADC reference. Repair cost is $195. We replace the DC-DC converter (Murata NME0505S). Turnaround is 7 days.

Q: Can I use the CTBDG1A with grounded thermocouples on a generator stator?
A: Yes – that is the primary application. Generator stators have high common mode voltages (up to 100 VAC induced on TC wires). Standard CTBA would fail. The CTBDG1A handles ±250 V common mode. However, ensure the TC insulation is rated for generator voltage. Use Teflon-insulated TCs (200°C, 600 V rated). PVC insulation will break down.

Q: How does per-channel CJC work?
A: Each of the 8 inputs has a small thermistor (NTC) mounted directly at the terminal block screw for that channel. The board measures each thermistor individually and applies compensation only to that channel. If one CJC thermistor fails (e.g., open circuit), only that channel is affected. Standard boards share one CJC for 8 channels – a single CJC failure corrupts 8 channels.

Q: How do I identify a counterfeit DS200CTBDG1A?
A: Genuine boards have “CTBDG1A” printed on the edge connector label. The isolation transformers are custom GE parts (yellow toroids, 8 total). Counterfeits often use generic transformers (black cubes) with lower isolation (500 V). Also check the CJC thermistors: genuine uses 8 separate NTCS0402 resistors. Fakes may have fewer. We photograph the isolation transformers on every board.

Q: What is the update rate for all 8 channels?
A: 240 ms total (30 ms per channel). The per-channel isolation adds settling time. Standard CTBA (non-isolated) updates in 20 ms per channel (320 ms for 16 channels). The CTBDG1A is slower per channel but faster for 8 channels because there are fewer channels to scan.

Q: Can I use the CTBDG1A with Type B thermocouples at high temperatures (1500°C)?
A: Yes – Type B is supported. However, Type B has very low output below 200°C. For ambient CJC, the board uses the per-channel thermistor (accurate to ±0.5°C). The low TC output at low temperature (<200°C) may cause noise susceptibility. For Type B, keep the reference junction (board) stable within ±2°C. Do not place the board near hot surfaces (>55°C).

Q: What is the maximum common mode voltage at 400 Hz (aircraft or high-speed generator)?
A: The isolation transformers are rated for 50/60 Hz operation. At 400 Hz, the transformer impedance increases, reducing common mode rejection. Maximum safe common mode voltage at 400 Hz is 50 V RMS (not 250 V). For 400 Hz applications, add external common mode chokes. We sell chokes for $35 per channel.

Q: Do you offer a version with conformal coating for offshore use?
A: Yes – special order DS200CTBDG1ABB (acrylic coated). Lead time is 14-21 days. Cost adds 75. Coated version is recommended for offshore and coastal sites. The isolation transformers are already potted – coating only protects the PCB. For offshore, also specify gold-plated terminal block (25 extra) to prevent screw corrosion in salt fog.

Q: What is the expected life of the isolation transformers?
A: The transformers have no moving parts. Rated life is 20+ years. Failure mode is usually broken lead wires from vibration or corrosion. For high-vibration applications (gas turbine skids), we reinforce transformer leads with silicone adhesive on all refurbished CTBDG1A boards. For corrosion, use conformal coating. The transformers themselves are potted and sealed.

PM591
PM571-ETH
PM581-ARCNET
PM581-ETH
PM582-ARCNET